I have a source document: - xslt-2.0

Question

I have a source document:
<?xml version = "1.0" encoding = "UTF-8"?>
<Circuit revision="B" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Block name="Design">
<Data>
<Layer name="INDEX_4" Function="PLANE"></Layer>
<Layer name="INDEX_9" Function="CORE"></Layer>
<Group name="PRIMARY">
<SubGroup name="GROUP_PRIMARY">
<SubLayer Ref="INDEX_4" thickness="0.0350"></SubLayer>
<SubLayer Ref="INDEX_9" thickness="0.1000"></SubLayer>
</SubGroup>
</Group>
</Data>
</Block>
</Circuit>
This stylesheet using current() extracts the corresponding thickness:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="xs"
version="2.0">
<xsl:template match="/Circuit/Block/Data/Layer">
<xsl:element name="{name()}">
<xsl:attribute name="id">
<xsl:value-of select="#name"/>
</xsl:attribute>
<xsl:attribute name="Function">
<xsl:value-of select="#Function"/>
</xsl:attribute>
<xsl:value-of select="/Circuit/Block/Data/Group/SubGroup/SubLayer[#Ref=current()/#name]/#thickness"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
Here's the second stylesheet to extract the PREVIOUS thickness value:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="xs"
version="2.0">
<xsl:template match="/Circuit/Block/Data/Layer">
<xsl:element name="{name()}">
<xsl:attribute name="id">
<xsl:value-of select="#name"/>
</xsl:attribute>
<xsl:attribute name="Function">
<xsl:value-of select="#Function"/>
</xsl:attribute>
<xsl:value-of select="/Circuit/Block/Data/Group/SubGroup/SubLayer[#Ref=preceding-sibling::*[1]/#name]/#thickness"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
In both cases I get this:
<?xml version="1.0" encoding="UTF-8"?>
<Layer id="INDEX_4" Function="PLANE">0.0350</Layer>
<Layer id="INDEX_9" Function="CORE">0.1000</Layer>
I tried the preceding-sibling to get the preceding value - I guess the question is "What is the context of the preceding-sibling?"
Is it the group with the Layer element or the group with the SubLayer element?
Thanks
Ralph B

Answer 1

Within any predicate the context item is the selected item in the step before the predicate so with SubLayer[#Ref=preceding-sibling::*[1]/#name] the context for both #Ref as well as preceding-sibling::*[1]/#name is the SubLayer element. If you want to select relative to the currently matched Layer element in the template you need to use current()/preceding-sibling::*[1]/#name inside the predicate.